1. Field of the Invention:
The present invention is concerned with a permanent magnet alloy comprising cobalt and at least one of the rare earth (RE) metals together with copper and/or aluminum. This invention is further concerned with a method of producing the permanent-magnet alloy and with uses thereof.
2. Description of the Prior Art
Hard-magnetic materials comprising inter-metallic compounds of cobalt with rare earths are known in numerous forms. The most developed, SmCo.sub.5 (1/5), magnets exhibit inner coercive field strengths, .sub.I H.sub.C, of 20 KOe and more, along with remanence values, Br, of 9 KG. Such hard magnets, produced both from the melt and by powder metallurgy, have been described in numerous publications (e.g., D. L. Martin and M. G. Benz, Permanent-Magnet Alloys of Cobalt with Rare Earths, Kobalt 50, 10, 1971). On the other hand, the Sm.sub.2 CO.sub.17 (2/17) alloys have had little commercial use for making permanent magnets. This is mainly due to their partially poorer primary-magnetic properties as compared to those of the 1/5 types, particularly with respect to the anisotropy field, H.sub.A, and due to the technological difficulties in making acceptably hard magnets using such alloys. Therefor, it has long been attempted to improve the primary properties, anisotropy field, H.sub.A, and saturation magnetization, M.sub.s, of (2/17) alloys by adding other elements to the alloy. Moreover, attempts have been made to optimize these values in finished hard magnets by incorporating suitable production steps. The effect of such additives on the properties is known from various publications (e.g., Nesbitt et al, Appl. Phys. Letters, vol. 12, pp. 361-362, June 1968; Ray et al, USAF Material Laboratory, Wright-Patterson Air Force Base, Ohio, AFML-TR-71-53, 1971; 71-210, 1971; 72-99, 1972; 72-202, 1972; 73-112, 1973; Senno et al, in DT-OS 2,406,782 IEEE Transactions on Magnetics, vol. MAG 10, No. 2, June 1974).
From the production technology side, in connection with the powder-metallurgic manufacture of SmCo.sub.5 hard magnets, there is known first of all the so-called "sintering with liquid phase" method (Benz et al, Appl. Phys. Letters 17,176,1970). It is known further that magnetic hardening of the alloy by addition of copper is largely independent of the parameters which govern the usual methods of choosing particle size. In particular, the troublesome and expensive fine grinding process can be avoided (e.g., Proceedings of the 3rd European Conference on Hard Magnetic Materials, Amsterdam 1974, p. 149).
Significantly detracting from the exceptionally hard-magnetic properties of the SmCo.sub.5 alloys is their high price. On the other hand, for special applications such as loudspeakers and electrical machines, there is a strong need for higher remanence permanent magnets. There are indeed hand-magnetic alloys with remanence values above 12 KG, but their coercive field strengths are under 1 KOe. This limits their applicability to devices with only very weak demagnetizing counter fields. In contrast, the 2/17 materials exhibit a more favorable demagnetization curve, and thus can be better used for the above mentioned purposes. Up to now, the 2/17 alloys have scarcely been used for the production of permanent magnets, since the magnetic properties achieved with them were unsatisfactory.
From the point of view of the process of preparing the alloys, the desire is for the most far-reaching simplification, economization and shortening possible. In order to obtain acceptable sintered pieces by powder metallurgy, more or less high proportions of samarium-rich sinter additives must be mixed into the starting material in practically all known methods, whereby the end product is made expensive both material and process-wise.